The concept of perceived risk plays a critical role in several models of health behavior and in much medical and psychological research. Models of risk judgment, such as the risk-as-feelings hypothesis, posit that risk perception is influenced by factors such as mood and emotions, factors that shift over the short and long term. These models and the supporting research lead to the prediction that if risk perception is influenced by naturally changing mood and emotions, then risk perception will also fluctuate over time. However, to date, this prediction has remained unexamined, despite its importance for patient decision making. Specifically, patient involvement in their medical decisions has been increasingly advocated, especially for prostate cancer screening decisions, because of the uncertainty surrounding the value of screening and the value-laden trade-offs involved in the decision. Because risk perception influences medical decisions, fluctuations in risk perception may lead to fluctuations in screening preference, making it difficult for patients to make a final decision. Thus, the purpose of this study is to conduct an initial examination of the prediction that among men deciding about prostate cancer screening, prostate cancer risk perception and screening preference fluctuate over time. The study will examine the nature and degree of risk perception and preference fluctuation, the correlates of fluctuation, and the impact of fluctuation on patients' final screening decision and decision conflict. Men attending an educational session on prostate cancer screening will be recruited to participate in the study. The Ecological Momentary Assessment technique will be used, with twice daily alerts from a personal digital assistant given to each subject, to assess daily change in prostate cancer risk perception, screening preference, mood and prostate cancer worry over a two week period. This study represents the first step in a rigorous research program exploring risk perception and preference fluctuation and their impact on decisions in prostate cancer screening, diagnosis and treatment.